U.S. patent number 6,063,216 [Application Number 09/134,561] was granted by the patent office on 2000-05-16 for working of a metallic strip.
This patent grant is currently assigned to Trico Products Corporation. Invention is credited to Oliver F. R. A. Damm, Warwick John Green, Lillian Hristov Ivanchev, Walter Luigi Trevisan.
United States Patent |
6,063,216 |
Damm , et al. |
May 16, 2000 |
Working of a metallic strip
Abstract
This invention relates to the working of a metallic strip. More
particularly, the invention relates to a method of working a length
of metallic strip by heat treating under tensile force, to a length
of metallic strip and to an apparatus for use in working a length
of metallic strip.
Inventors: |
Damm; Oliver F. R. A.
(Pretoria, ZA), Green; Warwick John (Penetanguishane,
CA), Ivanchev; Lillian Hristov (Germiston,
ZA), Trevisan; Walter Luigi (Johannesburg,
ZA) |
Assignee: |
Trico Products Corporation
(Buffalo, NY)
|
Family
ID: |
25586545 |
Appl.
No.: |
09/134,561 |
Filed: |
August 14, 1998 |
Foreign Application Priority Data
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|
|
|
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Aug 15, 1997 [ZA] |
|
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97/7365 |
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Current U.S.
Class: |
148/645; 148/320;
148/648; 266/254; 266/249; 148/646 |
Current CPC
Class: |
B21D
11/20 (20130101); B21D 25/02 (20130101) |
Current International
Class: |
B21D
11/00 (20060101); B21D 11/20 (20060101); B21D
25/00 (20060101); B21D 25/02 (20060101); C21D
008/02 (); C21D 009/84 () |
Field of
Search: |
;148/645,646,648,320
;266/249,259 |
References Cited
[Referenced By]
U.S. Patent Documents
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|
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3857741 |
December 1974 |
Hultgren et al. |
5875672 |
March 1999 |
Fourie et asl. |
|
Primary Examiner: Jenkins; Daniel J.
Assistant Examiner: Coy; Nicole
Attorney, Agent or Firm: Nixon & Vanderhye PC
Claims
What is claimed is:
1. A method of working a length of metallic strip, for a support
beam for a windscreen wiper blade which includes the steps of
positioning the strip on a former; and heating the strip while
subjecting the strip to tensile force to shape the strip to a
predetermined shape.
2. The method as claimed in claim 1 wherein the positioning causes
the strip to seat snugly on the former and restricts the strip to
the predetermined shape.
3. The method as claimed in claim 2, in which the force is applied
for the duration of the heating.
4. The method as claimed in claim 2, in which the magnitude of the
force is adjustable in order to accommodate expansion and shrinkage
of the strip during heating.
5. The method as claimed in claim 2, in which the former has a
convex upper surface and the strip is positioned on the surface
with its ends projecting beyond ends of the upper surface with the
tensile force being applied to said projecting ends.
6. The method as claimed in claim 2, in which the tensile force is
applied by pneumatic means.
7. The method as claimed in claim 1, in which the heat treatment
process includes a first heating step in which the strip is rapidly
heated to a temperature above transformation temperature.
8. The method as claimed in claim 7, which includes the step of
quenching the strip after the first heating step whilst it is on
the former.
9. The method as claimed in claim 7, in which the strip is
subjected to at least one further heating step for stress relief,
tempering or ageing, with the further step or steps being conducted
at a lower temperature than the transformation temperature.
10. A length of worked metallic strip which is substantially
residually stress free and which is produced by the method as
described in any one of claims 1 to 9.
11. The worked strip as claimed in claim 10, which comprises a
support beem for a windscreen wiper blade assembly.
12. The worked strip as claimed in claim 10, which has a yield
strength of between 650 MPa and 220 MPa.
13. An apparatus for use in working a length of metallic strip
which includes a former for forming the strip into a predetermined
shape in accordance with the method as claimed in any one of claims
1 to 9.
14. The apparatus as claimed in claim 13, in which the former has
an elongate, convex shaped, upper surface.
15. The apparatus as claimed in claim 13, which includes a
restricting means for restricting the strip in position on the
former.
Description
SUMMARY OF INVENTION
This invention relates to the working of a metallic strip. More
particularly, the invention relates to a method of working a length
of metallic strip, to a length of metallic strip and to an
apparatus for use in working a length of metallic strip.
According to a first aspect of the invention, there is provided a
method of working a length of metallic strip, which includes the
steps of
positioning the strip on a former; and
forming the strip on the former into a predetermined shape while
subjecting it to a heat treatment process.
The method may include the step of applying a tensile force to each
end of the strip after positioning the strip on the former, thereby
causing the strip to seat snugly on the former and restricting the
strip to the predetermined shape. The force may be applied for the
duration of the heat treatment process.
The magnitude of the force may be adjustable in order to
accommodate expansion and shrinkage of the strip in the heat
treatment process. The force may be adjusted so as not to exceed
the yield point of the thinnest sections of the strip at any time
during the working of the strip.
The former may have a convex upper surface and the strip may be
positioned on the surface with its ends projecting beyond ends of
the upper surface with the tensile force being applied to said
projecting ends.
The force may applied by pneumatic means, by suspending a weight
coupled to a spring to each of the ends of the strip, or the
like.
The step of forming the strip into the predetermined shape while
subjecting it to a heat treatment process may be controlled by a
processor.
The step of positioning the strip may include locating the strip on
the former such that a locating means of the strip corresponds with
complementary locating formations on the former.
The method may include controlling oxidation of the strip by
conducting the heat treatment process in a neutral atmosphere, such
as a nitrogen atmosphere.
The heat treatment process may include a first heating step in
which the strip is rapidly heated to a temperature above a
transformation temperature, In the case where the metallic strip is
formed of a ferrous material, this step may include heating of the
strip to above its an austenite transformation temperature. The
strip may be heated to a temperature of between about 900.degree.
C. and 1100.degree. C., more particularly to a temperature of about
1050.degree. C.
The method may further include the step of quenching the strip
after the first heating step whilst it is on the former. The strip
may be quenched in a controlled cooling process to a temperature
required to form martensite.
The strip may be subjected to at least one further heating step for
stress relief tempering or ageing, or the like, with the further
step or steps being conducted at a lower temperature than the
transformation temperature. It will be appreciated that in the case
of the metallic strip comprising a ferrous material, each of the
further heating steps is conducted at a lower temperature than the
austenite transformation temperature. One of the heating steps may
comprise a tempering step, in which the strip is heating and cooled
to form tempered martensite. Thus, the strip may be heated to a
temperature of between 400.degree. C. and 700.degree. C., and
preferably to a temperature of between 500.degree. C. and
600.degree. C. It will be appreciated that the temperature to which
the strip is heated is determined by the steel grade, the heating
rate of the strip and degree of hardness required. The strip may
then be allowed to cool.
Heating of the strip in all the steps of the heat treatment process
may be done by means of induction heating, gas heating, heating in
a radiant heat furnace or by a radiant heat, or the like.
Cooling of the strip in all of the heat treatment process steps may
be by means of a fine water spray, air, or with a solution
containing a polymer, or the like.
According to a second aspect of the invention there is provided a
length of worked metallic strip which is substantially residually
stress free and which is produced by the method as described
above.
The worked strip may have a thickness which varies along its length
in a ratio of at least 2:1, with its ends being the thinnest
sections of the strip. In a preferred embodiment, the thickness of
the strip may vary in a ratio of 2,7:1.
The width of the strip may also vary along its length, so that each
strip tapers inwardly, uniformly and continuously in both thickness
and width from its centre to its ends.
The worked strip may comprise a support beam for a windscreen wiper
blade assembly.
The worked strip may have a hardness of between 30 HRC and 60 HRC
and a yield strength of between 650 MPa and 220 MPa.
According to a third aspect of the invention, there is provided an
apparatus for use in working a length of metallic strip which
includes a former for forming the strip into a predetermined shape
in accordance with the method as described above.
The former may be manufactured from a material having a low thermal
expansion co-efficient and a low heat conductivity, such as a
ceramic material.
The former may have an elongate, convex shaped, upper surface. The
upper surface of the former may taper inwardly, uniformly and
continuously in width from its centre to its ends.
The apparatus may also include a restricting means for restricting
the strip in position on the former.
The invention is now described by way of example with reference to
the accompanying diagrammatic drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a schematic side view of apparatus for use in working
a length of metallic strip, in accordance with one aspect of the
invention;
FIG. 2 shows a schematic plan view of a former forming part of the
apparatus of FIG. 1;
FIG. 3 shows a sectional end view of the apparatus taken along line
III--III in FIG. 1;
FIG. 4 shows an enlarged schematic view of the encircled part of
FIG. 3; end
FIG. 5 shows a sectional end view of the apparatus taken along line
V--V in FIG. 1; and
FIG. 6 shows an enlarged schematic view of the encircled part of
FIG. 5.
DETAILED DESCRIPTION
Referring to the drawings, apparatus in accordance with the
invention, for use in working a length of metallic strip, is
designated generally by the reference number 10.
The apparatus 10 includes a former 12 of a ceramic material. The
former 12 has an elongate, convex shaped upper surface 14, which
tapers inwardly, uniformly and continuously in width from its
centre to its ends 16 and 18. The variation in width of the upper
surface 14 of the former 12 is clearly illustrated in FIG. 2 of the
drawings.
A length of metallic strip 20 is located on the former 12, with
ends 22 extending beyond the ends 16 and 18 of the former 12. The
apparatus 10 further includes a pair of pneumatic cylinders 24,
with a cylinder 24 being connected to each end 22 of the strip
20.
As illustrated in FIGS. 3 to 6, the thickness and width of the
strip 20 also varies along its length, so that each strip 20 tapers
inwardly, uniformly and continuously in both thickness and width
from its centre to its end 22.
The dimensions of the strip are as follows:
length=450 mm (plus an additional predetermined length of strip at
each end, which is used for attachment to the hydraulic cylinders.
The
additional lengths are cut off after treatment of the strip)
thickness at the centre=1.29 mm
thickness at the ends=0.30 mm
width at the centre=11 mm; and
width at the ends=6 mm
The apparatus 10 also includes a pair of induction coil heating
elements 26 which are located proximate the upper surface 14 of the
former 12.
In use, the metallic strip 20 is located on the upper surface 14 of
the former 12. Each of the ends 22 of the strip 20, is attached to
one of the pneumatic cylinders 24. The strip 20 is then cold formed
on the former 12 by exerting a tensile force on the ends 22,
causing the strip 20 to seat snugly on the upper surface 14 and
thereby forming a substantially curved strip 20. The force is
maintained at just below the yield point of the thinnest sections
of the strip and is in the region of about 80N. The strip 20 is
restricted in this position and subjected to a heat treatment
process.
The strip 20 is rapidly heated by the elements 26 to a temperature
of about 1050.degree. C., thus overshooting the austenite
transformation temperature. The strip 12 is quenched by means of a
fine water spray to a temperature required to form martensite.
Within 0.5-2 seconds after initiating the quenching of the strip,
the tensile force is gradually increased to between 250 N and 450
N.
The strip 20 is then tempered by heating the strip to a temperature
of about 400.degree. C. for a period of about 5 seconds to from
temper martensite. The strip 20 is allowed to cool and is removed
from the former 12. During the tempering step, the tensile force is
maintained at between about 250 to 500 N, and more particularly
between 250 N and 300 N.
The applicant believes that one of the advantages of the invention
is that the method combines the shaping and heat treatment of a
product in a single step, thereby eliminating the need to shape the
product after a heat treatment process, which creates further
stresses. It is clear that the combination of forming and
subjecting the strip to a heat treatment process determines the
final shape and mechanical properties such as hardness, strength,
toughness, and the like. In addition, the fact that the strip is
subjected to a tensile force for at least a part of the heat
treatment process, such as the tempering step, assists in forming a
substantially residually stress free product.
* * * * *